No abstract

Background: Acute kidney injury (AKI) portends worse prognosis following sepsis, with limited available interventions. Host iron acquisition by pathogens and systemic inflammatory response are key events in the pathogenesis of sepsis. In sepsis, hepcidin induces iron sequestration to limit iron availability to pathogens. Hepcidin is also known to limit inflammation. Since its role in pathophysiology of sepsis-associated AKI is unknown, we investigated the effect of exogenous hepcidin in endotoxin- and peritonitis-induced pathology and AKI. Methods: C57BL/6 mice were treated with saline or 50–100 µg of hepcidin, pre- and post-LPS injection, or cecal ligation and puncture (CLP, model of peritonitis). Splenectomized mice were challenged with LPS, with and without hepcidin. Mice were euthanized at 24 h after LPS injection and at different time points after CLP. Systemic inflammation and renal injury markers were assessed. Direct effect of hepcidin on renal tubular and endothelial cells was evaluated using endotoxin-induced cytotoxic serum. Role of heavy chain ferritin (H-ferritin) in mediating hepcidin-induced anti-inflammatory effect on LPS stimulated macrophages was evaluated with siRNA studies. Results: Twenty-four hours pretreatment with hepcidin significantly reduced LPS-induced AKI. Hepcidin ameliorated LPS-induced increase in serum TNFα and renal Cox-2, and prevented loss in PGC1α and cytochrome c oxidase activity. This was associated with reduced glomerular injury and preserved mitochondrial structure. Hepcidin did not exert direct protection on the renal parenchymal cells but reduced endotoxin-induced serum cytotoxicity to mitigate renal injury. Splenectomy reduced LPS-induced early inflammation and AKI, independent of hepcidin, indicating the importance of systemic inflammation. Higher splenic H-ferritin in hepcidin-treated animals was associated with reduced splenocytes apoptosis and inflammation. Hepcidin reduced LPS-induced IL-6 secretion in macrophages in H-ferritin dependent manner. Hepcidin significantly reduced CLP-induced AKI, and mortality (20% hepcidin treated vs 80% PBS treated). Importantly hepcidin reduced bacteremia and AKI even when administered after onset of sepsis. Conclusion: We demonstrate a protective role of hepcidin in endotoxin- and peritonitis-induced pathologies and AKI, exerted primarily through its anti-inflammatory effects, and antibacterial property. Macrophage H-ferritin plays an important role in hepcidin-mediated protection against endotoxin-induced inflammation. We uncover a novel prophylactic and therapeutic role of hepcidin in sepsis-associated bacteremia, AKI, and mortality.

Nephritis is a common manifestation of systemic lupus erythematosus, a condition associated with inflammation and iron imbalance. Renal tubules are the work horse of the nephron. They contain a large number of mitochondria that require iron for oxidative phosphorylation, and a tight control of intracellular iron prevents excessive generation of reactive oxygen species. Iron supply to the kidney is dependent on systemic iron availability, which is regulated by the hepcidin-ferroportin axis. Most of the filtered plasma iron is reabsorbed in proximal tubules, a process that is controlled in part by iron regulatory proteins. This review summarizes tubulointerstitial injury in lupus nephritis and current understanding of how renal tubular cells regulate intracellular iron levels, highlighting the role of iron imbalance in the proximal tubules as a driver of tubulointerstitial injury in lupus nephritis. We propose a model based on the dynamic ability of iron to catalyze reactive oxygen species, which can lead to an accumulation of lipid hydroperoxides in proximal tubular epithelial cells. These iron-catalyzed oxidative species can also accentuate protein and autoantibody-induced inflammatory transcription factors leading to matrix, cytokine/chemokine production and immune cell infiltration. This could potentially explain the interplay between increased glomerular permeability and the ensuing tubular injury, tubulointerstitial inflammation and progression to renal failure in LN, and open new avenues of research to develop novel therapies targeting iron metabolism.

Acute Kidney Injury (AKI) is a frequent complication of sepsis and an important cause of morbidity and mortality worldwide. A cornerstone of sepsis-associated acute kidney injury (SA-AKI) is dysregulated inflammation leading to increased tissue oxidative stress and free radical formation which leads to multiple forms of cell death. DJ-1 is a peroxiredoxin protein with multiple functions including its ability to control cellular oxidative stress. Although DJ-1 is expressed prominently by renal tubules, its role in AKI has not been investigated. In this study we examined the effect of DJ-1 deficiency in a murine model of endotoxin-induced AKI. Endotoxemia induced greater kidney injury in DJ-1-deficient mice. Further, DJ-1 deficiency increased renal oxidative stress associated with increased renal tubular apoptosis and with expression of death domain-associated protein (DAXX). Similar to the in vivo model, in vitro studies, using a medullary collecting duct cell line (IMCD3) and cytotoxic serum, we show that serum obtained from WT mice results in increased expression of s100A8/s100A9, DAXX, and apoptosis in DJ-1 deficient iMCD3 cells. Our findings demonstrate a novel renal protective role for renal tubular DJ-1 during endotoxemia through control of oxidative stress, renal inflammation, and DAXX-dependent apoptosis.

Hypertension is associated with an increased renal expression and activity of the epithelial sodium channel (ENaC) and iron deficiency. Distal tubules absorb iron, causing perturbations that may influence local responses. In this observational study, we investigated the relationship between iron content and ENaC expression and activity using two cell lines and hepcidin knockout mice (a murine model of iron overload). We found that iron did not transcriptionally regulate ENaC in hepcidin knockout mice or in vitro in collecting duct cells. However, the renal tubules of hepcidin knockout mice have a lower expression of ENaC protein. ENaC activity in cultured Xenopus 2F3 cells and mpkCCD cells was inhibited by iron, which could be reversed by iron chelation. Thus, our novel findings implicate iron as a regulator of ENaC protein and its activity.

Background Lupus nephritis (LN) is an end-organ complication of Systemic lupus erythematosus and is more common in premenopausal women. Hepcidin, the master regulator of iron homeostasis, modulates inflammation and is negatively regulated by estrogen. Therefore, we hypothesized that exogenous hepcidin may reduce the severity and delay the onset of LN. Methods Pre-nephritic 8-week-old or nephritic 16-week-old MRL/lpr female mice were injected Hepcidin (50ug, i.p) or vehicle twice a week and markers of renal injury and inflammation were examined at 18 and 20 weeks of age. The direct effect of hepcidin on macrophages was studied in-vitro. Results Hepcidin reduced intrarenal iron accumulation, and increased H-ferritin. This was associated with reduced renal inflammation and immune cell infiltration, which collectively mitigated microalbuminuria and tubular injury, independent of immune complex deposits and autoantibodies. The increase in H-ferritin, was associated with a reduced number of renal Ki-67+-F4/80+ macrophages. In-vitro, hepcidin induced H-ferritin in macrophages and reduced labile (Fe2+) iron. H-ferritinhi macrophages proliferated less upon Mcsf-1 stimulation and secreted less IL-1b, and IL-6 upon TLR-3 activation. Hepcidin reduced microalbuminuria when administered to nephritic, 16-week-old mice without worsening lupus-associated anemia. Conclusions We have identified that hepcidin targets iron homeostasis and reduces cardinal pathogenic features of LN. Importantly, Hepcidin treatment ameliorates kidney disease in mice with established proteinuria. Thus, our data highlight that targeting cellular iron metabolism with hepcidin represents a promising and a new therapeutic strategy in LN.